Analysis of Hot- and Cold-Rolled Loads in Medium-Mn TRIP Steels
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, D.M. FIELD
, and D.C. VAN AKEN
The purpose of this work is to investigate the hot- and cold-rolling requirements to produce third-generation advanced high-strength steels (AHSS). Therefore, five medium-Mn (10 to 14 wt pct Mn) alloys that exhibit transformation-induced plasticity (TRIP) were compared to a commercially produced grade of AISI 1018 using hot- and cold-rolling experiments. Experimental data collected from a STANAT instrumented rolling mill was utilized to measure force and torque during hot- and cold-rolling. Experimental data were processed by a 1D analytical model, based on Orowan model, to determine rolling pressure. It was determined that pressures required to hot-roll TRIP alloys are 1.4 to 1.8 times greater than pressures for rolling AISI 1018 steel. Cold rolling of the medium-Mn TRIP steels was found to be 1.5 to 2.8 times greater than the AISI 1018 steel. Mechanical and microstructural characterization was also performed and the variation in rolling pressure was related to the starting microstructural constituents, and alloys containing greater starting quantities of e-martensite in the microstructure had higher flow stresses at equivalent rolling strains during cold rolling. https://doi.org/10.1007/s11663-019-01566-4 The Minerals, Metals & Materials Society and ASM International 2019
I.
INTRODUCTION
TR ansformation-induced plasticity (TRIP) steels produce exceptional combinations of tensile strengths and ductility, offering an opportunity for the development of cost-effective and light-weight parts for automotive applications.[1] Although there have been many studies showing mechanical and microstructural characteristics of TRIP steels, few investigations have focused on the requirements to hot and cold roll these materials to produce the final condition being investigated. Quench and Partitioning (Q&P) has been shown to produce steels with high strength and formability without significant changes to the standard alloy composition[2–6] by the partitioning carbon to the c-austenite during controlled cooling of the steel through the martensite start temperature (MaS ) with a subsequent isothermal hold to produce metastable c-austenite at room temperature. Metastable c-austenite will transform to a-martensite under the imposition of a stress or strain, and this provides an additional volume change that accommodates the imposed plastic strain. This characteristic behavior is why these steels are described as TRIP
M.F. BUCHELY, D.M. FIELD, and D.C. VAN AKEN are with the Department of Materials Science and Engineering. Missouri University of S&T, Rolla, MO 65409. Contact e-mail: [email protected] Manuscript submitted October 15, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
steels for transformation-induced plasticity. Q&P steels have been reported to obtain strengths in excess of 1500 MPa with total ductility ranging from 20 to 10 pct strain.[7–9] In an alternative method to obtain the desired increased strengths and ductility, steels alloyed with increased manganese contents (5 to 15 wt pct
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